Structural and tribological properties of the plasma nitrided Ti-alloy biomaterials: Influence of the treatment temperature

Plasma Enhanced Chemical Vapor Deposition (PECVD) based saddle field fast atom beam source is a potential method for the nitriding of the Ti-based alloy at low pressure. In this study, influence of the nitriding temperature on the structural and the tribological properties of the low-pressure plasma nitrided Ti-6Al-4V alloy have been investigated. The cross-sectional optical investigation of the nitrided samples confirmed presence of a compound nitrided layer when nitriding was performed at high temperature and growth of this layer was found increased as nitriding temperature increased. X-ray diffraction result showed that the formation of the TiN phase commenced at high temperature and the concentration of this phase found increased as nitriding temperature increased. X-ray Photoelectronic Spectroscopy result also confirmed existence of the TiN as well as the TiNxOy phase in nitride layer. Micro hardness tests showed temperature depended hardness properties of the nitrided samples and a noticeable increase in the hardness value was observed for sample nitrided at 900 °C. Pin-on-disk test result confirmed an improvement of the tribological property of the nitrided sample comparing with the untreated sample. However, the samples nitrided at high temperature exhibited significantly decreased of the friction co-efficient and the wear depth value compared with the untreated and the low temperature nitrided (temperature below 700 °C) samples.